1. Field of the Invention
The present invention is directed to technology for peripheral cards.
2. Description of the Related Art
Memory cards are relatively small removable cards that provide data storage. In most cases, but not required in all cases, the memory card is integrated circuit based. These memory cards plug into or are received by ports or connectors on electronic devices, including computing devices, cameras, mobile telephones, PDAs and other devices. One example of a memory card uses non-volatile memory. Electrical Erasable Programmable Read Only Memory (EEPROM) and flash memory are among the most popular non-volatile semiconductor memories. Some examples of memory cards includes CompactFlash™, MMC™, Smart Media, Secure Digital™, MiniSD and the Memory Stick.
A flash memory card is a memory card that has one or more arrays of flash memory cells. Some flash memory cards also include bit line decoders, word line decoders, a state machine, a controller and other circuitry. In many cases the controller will be implemented in a first semiconductor die, while the array of flash memory cells, bit line decoders, word line decoders, and state machine are implemented in a second semiconductor die. Over time, flash memory arrays have increased density by shrinking the size of an individual memory cell and by implementing greater numbers of memory cells in the array.
To maintain product reliability and customer satisfaction, manufacturers of memory cards will test the memory cards during the manufacturing process in order to determine if there are any manufacturing defects. In many cases, the user I/O pins on the memory card connect to the controller. However, a test performed during manufacturing typically seeks to directly access the memory array (bypassing the controller) in order to test each cell in the memory array. Additionally, more pins will allow for more efficient and complete testing of the relevant components of the memory card. Thus, many memory cards will include test pins, in addition to the user I/O pins. To protect the memory card from electrostatic discharge relative to the test pins and to protect the data on the card from being wrongfully accessed via the test pins, the test pins should not be exposed to the user of the memory card after the manufacturing process.
One example of a memory card is described in U.S. Pat. No. 6,410,355 (the '355 patent”), incorporated herein by reference in its entirety. In the '355 patent, a memory card using flash memory is manufactured with a set of test pins at one edge of the memory card. After the memory card is tested, the test pins are cut off of the memory card and the memory card is then packaged. While the device of the '355 patent has worked well, there is a need for an improvement. First, the test pins that are cut off use real estate on the circuit board. There is a trend to increase density on circuit boards; therefore, it would be advantageous to not use a portion of the circuit board for components that will not ship to customers. Second, if the memory card fails in the field, there are no test pins to test the device in order to determine why the memory card failed. Such tests following device failure allow a manufacturer of memory cards to improve device reliability and the manufacturing process.
Another example of a memory card using flash memory is the recently released Mini-SD Card. In one commercial version of the Mini-SD Card, the memory array is mounted on the top of the circuit board and the controller is mounted on the memory array. User I/O pins and test pins are formed on the bottom of the circuit board. After the memory card is tested, the circuit board (with the controller, memory array and other components) are enclosed by attaching a top lid to a bottom lid. Both the bottom lid and the top lid are made of a hard plastic, and are manufactured from a mold prior to enclosing the circuit board. After the top and bottom lids are made, the top lid is ultra-sonically welded to the bottom lid to enclose the circuit board (with the controller, memory array and other components). The bottom lid has an opening for the user I/O pins. The bottom lid does not have an opening for the test pins; therefore, the test pins are not exposed to users. There will be a small air gap between the bottom lid and the bottom of the circuit board. While this design works well, the top and bottom lids are relatively expensive to manufacture. Additionally, the lids are relatively bulky which limits how small the memory cards can be manufactured. The trend in the industry to further decrease the size of memory cards.
As the memory cards are made smaller, they become increasingly difficult to handle by a human. Additionally, as the memory cards are made smaller, small variations in the packaging will have a larger proportional effect on the card. For example, due to the size of the memory card in relation to a human hand and due to variations in manufacturing, very small memory cards may be difficult to insert and/or remove into ports or connectors on electronic devices.